1. Field of the Invention
The present invention relates to a measuring apparatus and measuring method for measuring axis tilt of a shaft of a motor for a polygon mirror, and more particularly, to a measuring apparatus and measuring method for measuring axis tilt of a shaft of a motor for a polygon mirror in a non-contact manner.
2. Description of the Related Art
Recently, in a case where axis tilt of a shaft of a motor for a polygon mirror is measured, for example, the measurement is performed by the following. First, a plate mirror is attached to a leading end of a shaft so that the plate mirror is disposed in a direction perpendicular to an axial direction of the shaft. Next, inclination of the mirror is detected by using an autocollimator. In this way, axis tilt of the shaft is computed.
In addition, for example, Japanese Patent Unexamined Publication No. 60-211302 discloses a method for measuring an inclination angle of an object to be measured, the object having a columnar smooth outer peripheral surface. This measuring method measures the inclination angle of the object to be measured in a non-contact manner, and then computes a tilt angle of the columnar object to be measured based on the measured inclination angle. The measuring method disclosed in Japanese Patent Unexamined Publication No. 60-211302 will now be described in detail with reference to FIG. 8.
As shown in FIG. 8, a laser beam emitted from light source 101 is irradiated onto object 103 to be measured through optical axis 102, and is radially reflected. The reflected light includes a reflected light proceeding along a direction (returning along a direction of light source 101) of optical axis 102, a reflected light proceeding along first light path 104 having an angle of α with respect to the optical axis 102, and a reflected light proceeding along second light path 105. The reflected light proceeding along first light path 104 is reflected upward by first mirror 106, and first image sensor 107 receives the light. Further, the reflected light proceeding along second light path 105 is reflected upward by second mirror 108, and second image sensor 109 receives the light. Further, the reflected light proceeding along the direction of optical axis 102 is reflected upward by half mirror 110, and third image sensor 111 receives the light. The tilt angle of the object to be measured is computed based on three relative positions detected by three image sensors.
With the method disclosed in the Patent Document 1, in order to detect a Y-axis component of the axis tilt, third image sensor 111 for Y-axis measurement has to be installed in the direction of a light source position. Further, in order to avoid superposition between third image sensor 111 and light source 101, the path of the reflected light is changed by using half mirror 110. For this reason, an optical system such as half mirror 110 is required. In order to eliminate influences such as an installation error of the optical system, there is a problem in that an object to be measured which is used for correction and has no axis tilt has to be prepared to perform offset adjustment.